Cubic boron nitride (cBN) has such characteristics as hardness and heat conductivity that are next to diamond, and a low reactivity with iron-based metals in comparison with diamond. Because of the advantages in improving efficiency of processing, cBN sintered bodies containing cBN particles has come to take the place of conventional tools made of cemented carbide and cermet for cutting iron-based hard-to-cut materials.
Conventionally, as described in Patent Document 1, a cBN sintered body, formed by sintering cBN particles through a Ti-ceramic based bonding material, has been known. This sintered body, which has a comparatively low content of cBN particles, has a structure in which the cBN particles are sintered in a manner so as to be enclosed by the bonding material. Therefore, the mutual contact portions between the cBN particles are small. In contrast, another sintered body in which the content of cBN particles in the sintered body is increased so as to exert the features of the cBN, that is, high hardness and high heat conductivity, to the maximum degree has been known.
Patent Document 2 relates to a cBN sintered body in which the ratio of cBN particles is increased to provide a skeleton structure that allows the mutual cBN particles to be made in contact and reacted with each other. Patent Document 2 discloses the cBN sintered body formed by allowing cBN particles to react with each other and be bonded to each other with an Al-based alloy serving as a catalyst. This Patent Document also discloses a method in which, by using an Al alloy of Ni, Co, Mn, Fe, V or Cr as the bonding catalyst, the cBN particles are reacted with each other, while the Al alloy is reacted with the cBN particles, so that a sintered body is produced. Moreover, Patent Document 3 discloses a manufacturing method which provides a sintered body that has a greater content of cBN in the same manner as that of Patent Document 2, and is adjusted in the composition of the Al-based alloy to improve the sintering property so that the cBN sintered body can be obtained under a comparatively low pressure.
Furthermore, Patent Document 4 discloses a sintered body that is obtained by sintering only cBN particles and Al. Since, upon sintering, cBN and Al are allowed to react with each other to form aluminum nitride and aluminum diboride, this sintered body is made from cBN and the aluminum compound. The cBN in the sintered body has a skeleton structure in which the cBN particles are bonded to each other.    Patent Document 1: Japanese Patent Application Laid-Open No. 53-77811    Patent Document 2: Japanese Examined Patent Publication No. 52-43846    Patent Document 3: Japanese Examined Patent Publication No. 57-59228    Patent Document 4: Japanese Examined Patent Publication No. 63-20792